This invention relates to positive displacement compressors and, more particularly, to improved reciprocating compressors of the type for compressing air and other gases.
Positive displacement compressors are of the type in which successive volumes of air or other gas are confined within a closed space and are elevated to a higher pressure. Reciprocating compressors are positive displacement compressors of the type in which the pressure is increased as the volume of the closed space is decreased. There are many types of reciprocating compressors. They are used for such purposes as compressing air, refrigerants, various industrial gases, as well as in air conditioners and heat pumps.
Traditionally, although volumetric efficiency of reciprocating compressors has been a relatively important design consideration, it has had relatively little significance to the compressor user. However, owing to the increases in the price of electrical energy which is increased with the price of fossil fuels and general inflationary tendencies, and the need to provide greater performance for a given size of compressor and, thus, improve performance without increase in the cost of materials or manufacturing, volumetric efficiency has now become a matter of high concern.
Moreover, there has traditionally been substantial competition among compressor manufacturer representatives so that even relatively small increases in the volumetric efficiency and improvements of the overall efficiency of the compressors is a matter of great commercial concern, particularly since the users and purchasers of compressors are now increasingly conscious of such efficiencies. The effective power efficiency is a parameter by which compressors are sometimes now specified.
Effectively, the volumetric efficiency of a reciprocating compressor is the actual capacity (i.e., during the inlet stroke during which gas is drawn into the cylinder) to the piston displacement. Customarily, the volumetric efficiency is expressed as a percentage, the theoretical value of which for a given compressor is reduced by certain insufficiencies and losses.
It is an object of the present invention to provide an improved reciprocating compressor which may be utilized for compressing air and other gases, such as, for example, air conditioning, heat pumps, pneumatic compression, and for various other gas compression purposes.
It is a further object of the invention to provide such a compressor having increased volumetric efficiency with consequently improved effective power efficiency.
It is also an object of this invention to provide such a system for improving the efficiency of reciprocating compressors which can be readily incorporated into existing types of reciprocating compressors without drastic redesign or departure from the fundamental design concepts of such compressors.
The invention has as a still further object the provision of such a system for improving the efficiency of reciprocating compressors which utilizes relatively simple, reliable and mechanically straightforward components which can be readily incorporated into such compressors during manufacture, and which will not conduce to shortening of the design life of such compressors nor be prone to wear, mechanical failure or damage to a compressor during use.
It is also an object of the invention to provide such a system for improving the efficiency of reciprocating compressors which does not substantially interfere with the assembly or manufacture of such compressors and which can be readily incorporated during manufacture.
It is also an object of the invention to provide a device which can be utilized with existing compressor designs to modify the cylinder configuration of existing compressors without altering otherwise the method or principles of operation of the compressor to improve the volumetric efficiency characteristic of the compressor without change in the intrinsic displacement of the compressor.
Briefly, in accordance with the invention, the cylinder of a reciprocating compressor is provided with a flanged collar defining an annular recess adjacent the side walls of the cylinder bore. The disposition of this recess is such that the piston during its downstroke descends into the recess to compress gas therein. Communication is provided between this recess and the head space between the piston and cylinder head. As the piston descends, gas within the recess, being compressed, is provided through the communication to the head space to provide an increase in the initial pressure therein over what would be present in the absence of such an arrangement. Accordingly, during the piston upstroke, greater pressure is developed during the compression stroke, resulting in an increase in the volumetric efficiency of the compressor with concomitant decrease in the amount of theoretical displacement lost to the development of underpressure during a cycle of operation.